Separation systems commonly used in aerospace engineering and in other applications include releasable locking assemblies when interconnected mutually adjacent structures must subsequently be quickly and reliably disconnected. Examples of such structures are spacecraft and satellite launch vehicles, external fuel tanks, sensor booms, solar arrays, antennas, scientific equipment, and the like, which are used in the space program.
During the early days in the aerospace field, reliability of separation was the primary objective. If the fastener/separator failed to release on command, an entire project could be imperiled. However as use of the releasable locking assemblies increased so did the research effort. As a result of this widespread usage and research the reliability problems were solved.
Reliability is still a primary concern, but the problem per se having been solved, attention has been directed to improving separation devices. Much of the patent art is directed to these improvements. The separation devices have been developed in a variety of structures actuated to be separated by pneumatic, hydraulic or pyrotechnic forces generally resulting in mechanical shock. Bolts and nuts that can be cut or segmented to split on command by the actuated device are also the subject of patented improvements, examples being such patents as U.S. Pat. No. 6,406,074, U.S. Pat. No. 6,352,397, U.S. Pat. No. 5,671,650, U.S. Pat. No. 5,651,296, U.S. Pat. No. 5,248,233, U.S. Pat. No. 5,160,233, and U.S. Pat. No. 5,123,794.
Despite these improvements separation devices are still subject to certain limitations and disadvantages. One disadvantage is that pyrotechnic fasteners induce high stresses. Yet in order to drive pistons, or to fracture nuts or bolts, large shock loads must be produced by the explosive charge. Even the explosive force applied to segmented separation nuts can generate shock loads impacting on the assembly housing. As a load is applied to the bolt or nut, radial forces are generated which propel the segments so that they impact other components in the structures or in the separation device. This impact gives rise to particles or metal fragments having high kinetic energy that can lead to short circuits, mechanism jamming, damage to waveguides, and the like. To this end various improvements can now be found in the patent art for the reduction of release shock.
Another disadvantage has been brought to light by a NASA development. In the late 1990s NASA conceived the X-38 lifting body, along with a deorbit propulsion stage as a prototype for a full-sized crew return vehicle in the event of a catastrophic emergency that could require immediate evacuation from the Space Station. Desirably, each of the six joining bolts joining the lifting body to the deorbit propulsion stage should have a retraction time in the millisecond range. However rapid release in the case of separation mechanisms has not been as easily achievable as was imagined. Separation devices do not appear to lend themselves to improvements in the speed at which their two joined structures can be separated. Thus far it appears to have been achieved by limiting the lengths of the rods being retracted as suggested in U.S. Pat. No. 5,123,794. There is, then, room for improvement in this area as well. This invention is directed to such an improvement.